Coaxial line to strip line connector

ABSTRACT

A connector for coupling a coaxial cable and a strip line having compensating material in the launch area disposed in a slot extending diametrically across the face of a member that insulates a connecting rectangular tab from the connector body.

United States Patent [1 1 Q Donnell COAXIAL LINE T0 STRIP LINE CONNECTOR Inventor: John R. 0 Donnell, Ashland, Mass.

Assignee: EG & G, lnc., Bedford, Mass.

Filed: Sept. 10, 1973 Appl. No.: 395,486

US. Cl. 333/33, 333/97 R Int. Cl. H0lp 5/08 Field of Search 333/21 R, 33, 84 M, 97 R References Cited UNITED STATES PATENTS Voelcker 333/33 [451 July 23, 1974 3,553,607 1/1971 Leht'feld .333/84 M Primary Examiner-Paul L. Gensler Attorney, Agent, or Firm-Ralph L. Caclwallader, Esq.; Leo M. Kelly, Esq. v

[57 ABSTRACT A connector for coupling a coaxial cable and a strip line having compensating material in the launch area disposed in a slot extending diametrically across the face of a member that insulates a connecting rectangular tab from the connector body.

3 Claims, 13 Drawing Figures COAXIAL LINE T STRIP LINE CONNECTOR BACKGROUND OF THE INVENTION This invention relates to a coaxial line to strip line' v connector, and more particularly to a coaxial to strip line connector having compensating material in its launch area for compensating for impedance mismatch and phase shift.

In certain applications, it is necessary to connect a coaxial transmissionline (hereafter referred to as coaxial line) to a strip transmission line (hereafter rethe connector of FIG. 4 to a strip line;

lines from a connector and to machine the connector by trial and error thereby altering the physical dimensions of the connector to adjust for impedance mismatch and phase-shift. It is manifest that such a complicated procedure produces a connector tailored to operate only with a particular coaxial line and strip line.

- BRIEF DESCRIPTION OF THE INVENTION An object of this invention is to provide a new and improved coaxial line to strip line connector.

Another object is to provide a coaxial line to strip line connector havingcompensation for impedance mismatch and phase shift.

Briefly stated the foregoing and other objects and advantages of the invention are achieved through the provision of a hollow, tubular body terminating in a rectangular flange, a tubular insulator disposed therein provided with an axial bore and a contact member received in the axial bore. The contact member terminates in a narrow, rectangular tab to facilitate connecsimilar to the actual mode configuration of a strip line.

Additionally, introduction of the compensating material very close to the discontinuity introduced by a captivating plug has the effect of minimizing loss.

BRIEF DESCRIPTION OF THE DRAWING An understanding of additional aspects of the invention may be gained from a consideration of the followa ing detailed description of a preferred embodiment in 2 FIG. 3 illustrates the electric 'field configuration (TE mode) in a coaxial cable;

FIG. 4 illustrates a perspective view of a connector embodying the present invention;

FIG. 5 shows a.sectional view of the connector of FIG. 4;

FIG. 6 illustrates an end view of the connector of FIG. 4; v

FIG. 7 illustrates a sectional view of the body of the connector of FIG. 4;

FIG. 8 illustrates in section the tubular insulator of the connector of FIG.'4;

FIG. 9 illustrates the center contact, partially'in section, of the connector of FIG. 4;

. FIG. 10 illustrates, partially in section, connection of FIG. 11 presents curves useful in calculating cut-off wavelengths of higher modes of propagation of electric fields in coaxial transmission lines; and

FIGS. 12 and 13 present VSWR curves of the connector without and with compensating material in the launch area respectively.

Corresponding referencecharacters indicate corresponding parts throughout the several figures of the drawing.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 presents the conventional illustration of the electric lines of force 20 of the electric field of an electricwave propagating along a coaxial transmission line 22 in the TEM mode. Similarly FIG. 2 presents the conventional illustration of the electric lines of force 24 of the electric field of an electric wave propagating along conjunction with the accompanying figures of the ent invention as comprising a hollow, tubular body 34 terminating in rectangular flange 36, a tubular insulator 38 provided with an axial bore and a contact 40 received in the axial bore. FIGS. 4 and 7 show that body 34 has an exterior threaded portion 42adapted for connection to a coaxial cable, not shown; a centerbore 44 dimensioned to receive insulator 38 and apair of diametric holes 46communicating with bore 44 and located next to flange 36. FIGS. 5 and 8 show that tubular insulator 38 likewise has a pair of diametric holes 48 communicating with bore 50 and a slot 52 located in end face 54 of tubular insulator 38. Insulator 38 may be made of teflon. FIG. 9 illustrates contact 40 as having elongated cylindrical body 56 with a cylindrical slot 58 of reduced diameter, an end portion 60 having a counterbore 62 with a diametricslot 64 cut therein and the other end portion terminating in a narrow, rectangular tab 66.

In assembling connector 33, the side portions 65 opposite slot 64 of contact 40 are compressed slightly and contact 40 is then inserted into bore 500i insulator 38 until cylindrical slot 58 and holes 48 are in register with tab 66 extending beyond end face 54. The combination is then inserted into bore 44 of body 34 until holes 46,

holes 48 and slot 58 are in register, forming an aperture, with end face 54 flush with surface 37 of flange 36, as best seen in FIG. 5. Contact 40 is then turned until the plane of tab 66 has an orientation preferably perpendicular to slot 52, as shown in FIG. 6, although a parallel orientation has worked satisfactorily in one application, and other orientations may prove adequate in practice. Holes 46 and 48 and slot 58 are held in register and the aperture formed thereby is filled with a material that can be poured and hardened and which has a higher dielectric constant than that of insulator 38. The hardened material forms plug 68. Slot 52 is also filled with the same material denominated compensating material 70 in the drawing. After hardening of this material holes 46 are capped with a conductive material 72. Connector 33 is then ready for test and use. Tab 66 and slot 52 filled with compensating material 70 are denominated the launch area of connector 33.

' FIG. illustrates very diagrammatically the use of connector 33 with strip line 26. Strip line 26 has center conductor 28 spaced by insulating members 29 from outer conductive members 30. As shown, a pair of screws 27 form an electrical contact between flange 36 and conductive members 30 while, at the same time, maintaining tab 66 in good, tight, surface-to-surface, electrical contact with planar conductor 28 of strip line 26.

As stated above, the salutary effect of compensating material 70 is to pull the electric field of the coaxial cable (TEM mode) into a field concentration conducive to propagation of the TE mode and similar to the actual mode of propagation as shown in FIG. 2.

Those skilled in the art will recognize the captivation function of plug 68 and that this introduces a discontinuity between the coaxial and strip line conductors. A further salutary effect of compensating material 70 is that it is placed sufficiently close to this discontinuity 'to minimize loss, as hereinafter described.

Coaxial lines are usually operated with energy propagated in the principal, or TEM mode, and will transmit a wave of any frequency in this mode. But higher order modes of propagation can also exist. For these higher modes the coaxial line acts like a high-pass filter, and a given line will carry energy in one of the higher modes only if excited at a frequency above the critical or cutoff frequency for the given mode. This cut-off frequency depends upon the mode in question. At frequencies below cut-off, the higher modes may be excited at a source of energy or at a discontinuity in the line. In the present case such a discontinuity consists of plug 68. Such higher modes attenuate rapidly with distance and draw no real power. However, if another discontinuity is introduced at a point close enough to the first discontinuity, the loss is minimized. In the present case, such a second discontinuity consists of compensating material 70 in the launch area of connector 33. As shown in the example below for a 50 ohm connector the loss is less'than 1 db.

As an example, in connector 33 designed to connect a 50 ohm coaxial line to a strip line, the inner diameter of the outer conductor, denoted b in FIG. 5, is 0.161 inch and the outer diameter of the inner conductor, denoted a, is 0.050 inch. Hence the b/a ratio is 0.16l/0.050 or 3.22.

In FIG. 11, abscissas represent b/a ratios and ordinates represent ratios of )t /Zb where A, is the wavelength at the cutoff frequency for a particular mode of propagation in a coaxial line. Referring to curve 74 for the TE mode one finds that the A /Zb ratio for a b/a ratio of 3.22 is 2.0. Thus:

).,/2b 2 or A, 4b or A, 0.644 inch.

One then may solve for the cut-off frequency, F using the equation:

where F is in gigaherz. Thus:

P l1.808/ 11.808/0.644 18.34 Ghz Alternatively one may use the formula:

)t =1r [b+a] 3.1416[0.161+0.050]

=0.6629 inch and F 11.808/0.6629 17.81 Ghz The attenuation of any mode in the cut-off region is given by the formula:

where a is attenuation in db/unit length;

h is the wavelength of cut-off frequency; and )t is the wavelength of the frequency of interest. Thus,

at 17 Ghz using the above A, of 0.644:

)t 11.808/17 0.6945 inch; and

= 31.78 db/unit length.

The attenuation per wavelength at 1? Ghz thus is 31.73 X 0.6945 or 22.04 db/wavelength.

In one actual connector, built in accordance with the principles herein disclosed, the distance between captivation material 68 and compensating material 70 was 0.029 inch. Using the above value of a at 17 Ghz the attenuation therebetween was 31.73 X 0.029 or 0.92 db.

Comparative tests were made with the connector illustrated in FIGS. 4 and 5 and one having the same dimensions but without slot 52 in the end face 54 of tubular insulator 38, and thus, without compensating material 70. Curve of FIG. 12 illustrates the VSWR of the connector without compensating material. Curve 82 of FIG. 13, to the same scale as curve 80, illustrates significant improvement in VSWR achieved with the connector employing the present invention.

The width and depth of slot 52 vary inversely with the dielectric constant of compensating material 70. Compensating material 70 must have a dielectric constant greater than that of insulator 38. The dielectric constant of teflon is about 2.04. I have used an epoxy resin having a dielectric constant of 4.0. With materials having even greater dielectric constants, the width and depth of slot 52 would be decreased. It is believed that the effect of the increased dielectric constant is to more efficiently pull the electric field into the TE mode.

In view of the foregoing, it may be seen that the several objectsof the present invention are achieved and other advantageous results have been attained. While a preferred embodiment of the invention has been shown and described, it will be apparent to those skilled in the art that changes can be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims.

I claim:

1. A connector for coupling a coaxial cable to a strip the dielectric constant of the core member, filling the aperture and reduced diameter portion and holding the reduced diameter portion for preventing relative axial movement between the outer conductor, the core member and the center conductor;

the plug being formed from a material having a fluid state and pourable into the aperture to define, upon hardening, the solid plug;

the center conductor terminating in a thin rectangular, planar tab extending beyond the flange; and

the core member terminating at the tab in a slot filled with said hardened material. 2. A connector as in claim 1 in which the plane of the tab has an orientation perpendicular to the slot.

3. A connector as in claim 1 in which the plane of the tab has an orientation parallel to the slot. 

1. A connector for coupling a coaxial cable to a stripline comprising: a tubular outer conductor terminating at one end in a flange; a solid dielectric core member, having a dielectric constant, located within the outer conductor and having an axially extending central bore; the outer conductor and the core member having a radially extending aperture adjacent the flange; a cylindrical center conductor located within the central bore and having a reduced diameter section located within the aperture; a solid plug, having a dielectric constant greater than the dielectric constant of the core member, filling the aperture and reduced diameter portion and holding the reduced diameter portion for preventing relative axial movement between the outer conductor, the core member and the center conductor; the plug being formed from a material having a fluid state and pourable into the aperture to define, upon hardening, the solid plug; the center conductor terminating in a thin rectangular, planar tab extending beyond the flange; and the core member terminating at the tab in a slot filled with said hardened material.
 2. A connector as in claim 1 in which the plane of the tab has an orientation perpendicular to the slot.
 3. A connector as in claim 1 in which the plane of the tab has an orientation parallel to the slot. 